Generally speaking, U.S. Pat. No. 3,155,046 to Vaughan, issued Nov. 3, 1964, discloses a centrifugal pump having an open impeller with radial vanes. The vane edges adjacent to the pump inlet cooperate with sharpened edges of inlet apertures to cut stringy material or chunks entering the pump. Similarly, U.S. Pat. No. 3,973,866 to Vaughan, issued Aug. 10, 1976, and U.S. Pat. No. 4,842,479 to Dorsch, issued Jun. 27, 1989, disclose centrifugal pumps having impellers with vanes cooperating with inlet apertures to achieve a chopping or slicing action of solid material in a liquid or slurry being pumped. In the case of the pumps of U.S. Pat. No. 3,973,866 to Vaughan and U.S. Pat. No. 4,842,479 to Dorsch, however, semi-open impellers having radial shroud plates are used and external booster propellers may be provided to accelerate flow into the pump. The latter, when used, helps displace chunks of solid matter which become lodged in the inlet apertures and, at least in some instances, cuts solid matter prior to entry into the pump.
Other types of pumps having external cutters rotated with an impeller or propeller are shown in U.S. Pat. No. 2,714,354 to Farrand, issued Aug. 2, 1955; U.S. Pat. No. 3,325,107 to Peterson, issued Jun. 13, 1967; and French Patent No. 1.323.707, issued Mar. 1, 1962. U.S. Pat. No. 3,444,818 to Sutton, issued May 20, 1969, discloses another type of centrifugal pump having an internal impeller with vanes cooperating with the periphery of an inlet aperture to achieve a slicing action. In the Sutton construction, an outer “chopper member” has blades that wipe across the outer surface of the apertured intake plate to assist in chopping solid material to a size small enough to enter the intake aperture. Similarly, in the construction shown in British Patent No. 1,551,918, published Sep. 5, 1979, external blades sweep across small intake apertures to dislodge or gradually cut solid material clogging an intake aperture. In both the construction shown in the Sutton patent and the construction shown in the British patent, the external member is mounted so as to be moveable axially away from the intake plate if a hard obstruction is encountered.
Other types of pumps designed for pumping liquids or slurries containing solid materials are disclosed in Canadian Patent No. 729,917, issued Mar. 15, 1966; Schlesiger U.S. Pat. No. 3,340,812, issued Sep. 12, 1967; Elliott U.S. Pat. No. 4,527,947, issued Jul. 9, 1985; and Corkill U.S. Pat. No. 4,575,308, issued Mar. 11, 1986.
One of the problems with each of these devices is the occurrence of motor overloading during heavy chopping. Where the chopping is not efficient, the motor power increases causing the motor protection controls to trip the motor offline. When the motor goes offline, the chopping stops and operator intervention is required to place the motor back online. The chopping down-time, of course, detracts from the cost effectiveness of the process.
Another problem relates to excessive wear on the cutting parts over time. Fibrous material, such as hair and the like, tend to accumulate in the cutting area, particularly at the cutting parts. The fibrous material collects grit and sand causing the cutting parts to grind down prematurely. A cutter nut and cutter bar assembly at the pump intake has been used to keep the cutting parts clear of such fiber and debris.
Perhaps the most closely related device for this purpose is shown in U.S. Pat. No. 5,460,483 to Dorsch, issued Oct. 24, 1995. The Dorsch '483 patent illustrates a square cutter nut projection (60) in FIG. 12. FIG. 15 of Dorsch '483 better illustrates the cutting operation of the projection (60) as it passes fingers (41). However, such a configuration is not nearly as aggressive as the invention of the present disclosure.
It is therefore desirable to provide a cutter assembly which helps maintain a clear cutting area, reduces cutting part wear and improves chopping efficiency to reduce motor power load and chopping down-time. It also would be desirable to provide a cutter assembly which aggressively reduces the build-up and collection of grit in the cutting area. The disclosed device affords other structural, manufacture and operating efficiencies not seen in prior art devices, as well